Gloeophyllum sepiarium (Wulfen) P. Karst
Although this species has gills, it is a polypore.
A common polypore species in pine forests. It is a thin bracket with a distinctive undersurface of gill-like ridges as seen in the next image. Shelf size: 50–60 mm x 40–50 mm.
It is found on the wood of introduced conifers, and first observed here in the mid 1970's. It is a common fungus in the Northern Hemisphere.
The underneath side of this fungus.